Giamatti has joined the drama's fourth series as the brother of Lady Grantham.

Leech told BBC News: "We ended up in a Reading nightclub called Q. We were out quite late, we'd gone to dinner and [Paul] was like, 'Oh should we go for another drink?' Yeah, we'll go for another drink.

"We went up to this place and you could see people going, 'Am I just really drunk or is Paul Giamatti over there?'"

He continued: "This one guy just kept hugging him and we were on the dance floor and this guy just kept hugging him, and he turned to me and said, 'Big fan, big fan'.

"He was really cool and I think he enjoyed the night. We were all on set the next day, except for Paul - he had the latest call the next day.

"We were clever enough, we knew what we were doing. The girls [had] 5am pick ups - silly, silly, silly."

Downton Abbey returns for a fourth series on Sunday, September 22 at 9pm on ITV.